Gardeners in Michigan commonly come across hundreds of spider species with little to no circumstance -- and sometimes without even a notice -- while doing yard work and other outdoor chores. Although nearly every spider species in the world produces venom, only a few species in Michigan produce a painful or medically significant bite.
Nearly every spider species in Michigan can bite, but most refuse to do so. Placing your hand or other body part against a spider, getting too close to a spider's egg sac or having a spider crawl into your clothing are all scenarios that may warrant a bite.
If you receive a bite from a spider, safely collect the spider in a jar or other container. The saved specimen will aid in the positive identification of its species.
Clean a spider bite with mild soap and water, and then apply a cool compress to the wound. If you have pain, use an over-the-counter medication such as acetaminophen or ibuprofen; for itching, consider using an antihistamine. Seek immediate medical care if any of the following occur: severe pain, abdominal cramping or a craterlike, or ulcerlike, wound around the bite.
Northern Black Widow
Comb-footed spiders, sometimes called cobweb spiders, are in a family of web builders. In Michigan, one important species that belongs to this group is the northern black widow spider (Latrodectus variolus). The female has a shiny, black, globular abdomen with red marks. Unlike the southern black widow (Latrodectus mactans), which displays a red hourglass shape, the northern black widow has a row of red spots on the top of its abdomen and two red marks on its underside that may or may not combine in the shape of an hourglass.
Like other black widows, the northern black widow has a medically significant bite due to its neurotoxin venom.
Northern black widow rarely makes itself known to gardeners. It often places its irregular webs close to the ground, such as around loose bark, water spigots and tree stumps, or in protected outbuildings, such as barns and storage sheds. Although northern black widow isn't aggressive, touching a female's web often sends the spider into protective mode because an egg sac is typically in the web.
The equally famed and feared brown recluse spider (Loxosceles reclusa) isn't native to Michigan, although the small number of identified specimens of them found in Michigan may indicate isolated populations of them are throughout the state. Many times brown recluse spiders are found inside structures, not outside them. Brown recluse spiders are yellowish to dusky brown and often have a darker-brown, fiddle-shaped marking behind their six eyes.
A brown recluse spider's bite may produce few to no symptoms, or it may produce severe necrosis -- dying of tissue around the wound, resulting in a craterlike wound, discomfort and a large blister that develops over several hours. Many other factors can cause those symptoms, however.
One other potentially dangerous species found in the state is the yellow sac spider (Cheiracanthium inclusum).
The yellow sac spider is yellowish to creamy in color with dark brown on the tips of its feet and pedipalps -- antennaelike appendages near its mouth; it has a darker stripe running down its abdomen. As its common name implies, the yellow sac spider spins a silken retreat similar to a sac. The spider is nocturnal, often staying in its sac during the day or hiding under plant leaves.
This yellow sac spider species and another yellow sac spider species may account for more human bites than any other kind of spider. Their bites generally cause no problems, but some people sensitive to them may experience burning at the bite site, blistering within one to 10 hours, muscle cramps, nausea and fever; many of those symptoms are common with a black widow spider bite, too. The bite from a yellow sac spider also may result in tissue dying around the wound, similar to what occurs from a brown recluse spider bite.
Other Common Species
It's not uncommon to spot spider webs while working outside in Michigan. Whether they are the small webs of spined micrathena spiders (Micrathena gracilis) in forested yards or the large webs of black-and-yellow argiope spiders (Argiope aurantia), webs play a useful part in pest control for Michigan gardeners. Spined micrathena and black-and-yellow argiope spiders are members of the orb weavers group. Orb weavers spin geometric webs. These large orb weavers aren't typically aggressive but can produce painful bites when handled or cornered.
When pulling weeds or being low to the ground for another reason, you may cross paths with several species of large spiders. They include wolf spiders (Lycosidae), which are typically hairy and run quickly along the ground. These active hunters can give quite a scare to an unsuspecting gardener. They can produce a painful bite, but their venom is not considered dangerous unless the bite victim is allergic to it.
Grass spiders (Agelenopsis spp.), which are sometimes large, build sheetlike webs with an open-ended funnel in grass or other low vegetation. Although grass spiders may bite when handled or disturbed, their bites are not considered medically significant, and these fast spiders quickly dart from human interference.
Many spider species don't build webs but instead live on plants. Some, such as several species of crab spiders (Thomisidae spp.), have coloration that makes them look remarkably similar to their host plants. These spiders often ambush insect prey.